1. Field of the Invention
The present invention relates to a rotary encoder, especially, relates to a position-adjustment of photo-interrupters provided in the rotary encoder.
2. Description of the Related Art
Generally, a rotary encoder has a rotating disc and a pair of photo-interrupters, and detects a rotation position, namely, rotation-angle of a rotating member, such as a DC motor. The rotating disc rotates around a rotating-axis of the rotating member in accordance with the rotation of the rotating motor. The disc has slits, which are formed circumferentially at constant intervals, and is journaled around the rotating-axis. Each of the pair of photo-interrupters has a light-emitting device such as an LED, and a photo-detector such as a photo-diode. Then, each photo-interrupter is positioned so as to put the slits between the light-emitting device and the photo-detector.
When the DC motor rotates, the slits pass through the light-path between the light-emitting device and the photo-detector. Consequently, a sequence of pulse signals is output from each of the pair of photo-interrupters. The pair of photo-interrupters is positioned such that a phase deference between two sequences of pulse signals occurs, thus a rotation-amount and a rotation direction, namely, the rotation position of the disc is detected. The DC motor is controlled on the basis of the detected rotation position.
Since the rotation position is detected in accordance with the phase difference between two pulse signals, the precision of the detected position depends upon the relative position-relationship between the two photo-interrupters. However, the precision of the size or the form is different in each photo-interrupter. When the pair of photo-interrupters is not positioned at a desired place precisely, the rotation-position cannot be detected correctly.